1. Field of the Invention
This invention relates to a printing plate mounting apparatus, a printing plate replacement apparatus and a printing plate replacement method and can be utilized as a mechanism for mounting a sheet-like printing plate on a printing cylinder of a rotary printing press.
2. Description of the Related Art
Heretofore, in a rotary printing press ink is applied to a sheet-like printing plate mounted on a cylindrical printing press, and the printing cylinder is rotated to transfer ink from the printing plate to paper or the like and thus effect the printing.
For mounting such printing plate, a printing plate mounting mechanism is used, which winds a printing plate on the printing cylinder and take in and lock the ends of the printing plate with a lock shaft provided in the printing cylinder.
FIGS. 24 to 26 shows such a printing plate mounting mechanism 90. The mechanism comprises a lock shaft 93, which is provided in a cavity 92 formed axially in a printing cylinder 91 adjacent the surface thereof. The lock shaft 93 has an axially continuous slit 94, and an end of the printing plate 95 can be inserted in the slit 94 to be secured in the same.
The lock shaft 93 has an end portion projecting from an end face of the printing cylinder 91. A rotary block 81 is secured to the end portion. The rotary block 81 is secured in position by two pins 82 and 83 provided on the end face of the printing cylinder 91.
A counterpart block 84 is secured to the end face of the printing cylinder 91 at a position spaced apart from the rotary block 81. Between the counterpart block 84 and rotary block 81 is provided a compression coil spring 86, which is guided by a guide rod 85.
The components 81, 84, 85 and 86 constitute a toggle mechanism 80, which can hold the lock shaft 93 stably at two positions as shown in FIGS. 25 and 26.
When mounting the printing plate 95, the leading end of the printing plate 95 is inserted into the gap or clearance between the surface of the cavity 92 and the lock shaft 93 as shown at A in FIG. 25, the succeeding portion of the plate is wound on the printing cylinder 91 as shown at B, and the trailing end of the plate is inserted in the slit 94 as shown at C.
Then, the lock shaft 93 is rotated to take in the trailing end of the printing plate 95 inserted in the slit 94 while also taking in the leading end of the plate 95 in contact with the leading end as shown at D. Thus, the printing plate 95 is mounted in close contact with the surface of the printing cylinder 91 by tension from its opposite ends.
In such printing plate mounting mechanism 90, the lock shaft 93 is usually turned manually using a spanner or the like fitted on a hexagon nut (see FIG. 24) provided at the end of the lock shaft 93.
Meanwhile, recently there is an increasing demand for energy saving and automation, and it has been proposed to drive the lock shaft mechanically with a gear mechanism as shown in, for instance, Japanese Utility Model Laid-Open No. 27339/1990.
FIG. 27 shows such a printing plate mounting mechanism. This mechanism comprises a lock shaft 72 provided rotatably adjacent the surface of a printing cylinder 71. A small gear 71 is secured to an end of the lock shaft 72, and it is Meshed with a large gear 74. The large gear 74 is integral with an intermediate gear 75 and secured coaxially to an end of the printing cylinder 71. A rack 76 is meshed with the intermediate gear 75 in the tangential direction thereof.
The rack 76 is supported by a longitudinal drive cylinder 77 and also by an orthogonal drive cylinder 78. When the rack 76 is in its meshed state, it is advanced and retreated by the longitudinal drive cylinder 77 to rotate the lock shaft 722 via the intermediate gear 75, large gear 74 and small gear 73. For printing, it is de-meshed from the intermediate,gear 75 by the cylinder 78 so that it will not interfere with the rotation of the printing cylinder 71.
In such printing plate mounting mechanism 70, however, since the rack 76 for driving the lock shaft 72 is supported by the two cylinders 77 and 78, instability in structure and also in operation is inevitable, and de-meshing during operation is likely.
Further, since the operation of meshing of the rack 76 and intermediate gear 75 is effected in the orthogonal direction to the rack tooth face, failure of smooth meshing is likely.
Further, for ensuring smooth meshing it is necessary to operate the two cylinders 77 and 78 in an interlocked relation to each other, thus dictating complicated control.
To solve the above problems, the applicant has proposed a printing plate mounting mechanism, in which de-meshably meshed gears are supported on a shaft such that they can be meshed and de-meshed by displacing one of them along the shaft (Japanese Utility Model Application No. 77338/90).
In such printing pate mounting mechanism, the meshing and de-meshing of the gears are made with axial displacement, and also the lock shaft is rotated at a fixed position with the rotation of the gears about the shaft thereof. Thus, each operation may be performed independently. The stability of the operation of rotating the lock shaft and also at the time of the meshing of the gears can be enhanced, and reliable operation can be ensured with simple operation.
However, with the above printing plate mounting mechanism of the gear type noted above, it is possible to completely eliminate mutual catching of the gears even though the gears are meshed with axial displacement as noted above, and possible defective operation at the time of meshing the gears is inevitable.
Further, the above gear type printing plate mounting mechanism requires a printing cylinder side gear, a drive gear meshed and de-meshed with and from this gear, drive means for driving the drive gear to cause rotation of the lock shaft and means for controlling the meshing and de-meshing of the drive gear. Therefore, the complication and size increase of the mechanism are inevitable. Further, the space between the printing cylinder and the outer wall is narrow, and it is difficult to secure a space for installing a large size printing plate mounting mechanism along the end face of the printing cylinder. In other words, the installation of the mechanism requires great modification of the pertinent portion of the printing press.
In a further aspect, in the prior art printing plate mounting mechanisms noted above, although the ends of a printing plate wound on the printing cylinder periphery can be clamped, the printing plate is wound manually on the printing cylinder. More specifically, for winding the printing plate on the printing cylinder, it is necessary to insert and engage the leading end of the printing plate in the lock shaft, then wind the plate around the printing cylinder periphery by turning the cylinder, for instance, then insert the trailing end of the plate in the lock shaft and then clamp the plate with the printing plate mounting mechanism. Heretofore, these cumbersome operations are all done manually. Therefore, it is difficult to improve the operational efficiency when replacing the printing plate. In addition, there is high possibility of erroneous mounting or like because the operations are carried out manually. That is, reliable operation is impossible.
In the printer, the replacement of the printing plate is not automated while the other parts are automated variously. This has been posing problems in the operational efficiency improvement of the whole printer.
An object of the invention is to provide a printing plate mounting apparatus, which may be simple in structure and small in size and permits high stability to be obtained in operation.
Another object of the invention is to provide an apparatus for and method of replacing printing plate, which permit reliable and efficient replacement of a printing plate.